We compare the frequency of field binary stars as a function of Galactic velocity vectors , and find a deficiency of such stars on strongly retrograde orbits .
Metal-poor stars moving on prograde Galactic orbits have a binary frequency of 28 \pm 3 % , while the retrograde stars ’ binary frequency is only 10 \pm 2 % for V \leq - 300 km s ^ { -1 } .
No such binary deficiencies are seen for the U or W velocities , nor [ Fe/H ] .
Some mechanism exists that either disrupts binary systems or preferentially adds single stars moving primarily on retrograde orbits .

Theoretical analyses and critical evaluations of our observational data appear to rule out preferential disruption of pre-existing binary stars due to such causes as tidal interactions with massive gravitional perturbers , including giant molecular clouds , black holes , or the Galactic center .

Dynamically-evolved stellar ensembles , such as globular clusters , provide a possible source of single stars .
Three lines of evidence rule out this explanation .
First , there is no mechanism to significantly enhance dissolution of clusters moving on retrograde orbits .
Second , a study of globular clusters moving on prograde and retrograde orbits , and with perigalacticon distances such that they are unlikely to be affected strongly by central tidal effects , shows that clusters moving on prograde Galactic orbits may be more evolved dynamically than clusters moving on retrograde orbits .
Finally , we have undertaken a comprehensive search for star streams that might be disernible .
Monte Carlo modelling suggests that our sample may include one moving group , but it contains only five stars .
While the Galactic orbit of this group passes near the Galactic center , it is not moving on a retrograde Galactic orbit , and falls short by a factor of at least twenty in supplying the necessary number of single stars .

There is one intriguing possibility to explain our results .
A dissolved dwarf galaxy may have too large a velocity spread to be easily detected in our sample using our technique .
But dwarf galaxies appear to often show element-to-iron vs. [ Fe/H ] abundance patterns that are not similar to the bulk of the stellar field and cluster halo stars .
We explore the s -process elements Y and Ba .
Eight stars in our sample have such elemental abundances already measured and also lie in the critical domain with -1.6 \leq [ Fe/H ] \leq -1.0 and V \leq -300 km s ^ { -1 } .
The admittedly small samples appears to show a bimodal distribution in [ Y/Fe ] , [ Ba/Fe ] , and [ \alpha /Fe ] , where “ \alpha ” represents an average abundance of Mg , Si , Ca , and Ti .
This behavior is reminiscent of the difference in the abundances found between the globular cluster \omega Centauri and other globular clusters .
It is also intriguing that the stars most similar to \omega Cen in their chemical abundances show a relatively coherent set of kinematic properties , with a modest velocity dispersion .
The stars less like \omega Cen define a dynamically hot population .
The binary frequency of the stars in \omega Centauri does not appear to be enhanced , but detailed modelling of the radial velocity data remains to be done .